Vehicle occupant position and velocity sensor

ABSTRACT

An occupant position sensor utilizing either ultrasonic, microwave or optical technologies, or seatbelt spool out and seat position sensors, are used as inputs to the primary vehicle crash sensor circuit to permit the longest possible sensing time before the occupant gets proximate to the airbag and is in danger of being injured by the deploying airbag. The sensor further disables the inflatable restraint system if the occupant is in danger of being injured by the system deployment. Separate systems are used for the driver and passenger to permit the optimum decision to be made for each occupant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.08/505,036 filed Jul. 25, 1995 now U.S. Pat. No. 5,653,462, which inturn is a continuation of U.S. patent application Ser. No. 08/040,978filed Mar. 31, 1993, now abandoned, which in turn is acontinuation-in-part of application Ser. No. 08/878,571 filed May 5,1992, now abandoned.

BACKGROUND OF THE INVENTION

Crash sensors for determining that a vehicle is in a crash of sufficientmagnitude as to require the deployment of an inflatable restraintsystem, or airbag, are either mounted in a portion of the front of thevehicle which has crushed by the time that sensor triggering isrequired, the crush zone, or elsewhere such as the passengercompartment, the non-crush zone. Regardless of where sensors are mountedthere will always be crashes where the sensor triggers late and theoccupant has moved to a position near to the airbag deployment cover. Insuch cases, the occupant may be seriously injured or even killed by thedeployment of the airbag. This invention is largely concerned withpreventing such injuries and deaths by preventing late airbagdeployments.

In a Society of Automotive Engineers (SAE) paper by Mertz, Driscoll,Lenox, Nyquist and Weber titled “Response of Animals Exposed toDeployment of Various Passenger Inflatable Restraint System Concepts fora Variety of Collision Severities and Animal Positions” SAE 826074,1982, the authors show that an occupant can be killed or seriouslyinjured by the airbag deployment if he or she is located out of positionnear or against the airbag when deployment is initiated. Theseconclusions were again reached in a more recent paper by Lau, Horsch,Viano and Andrzejak titled “Mechanism of Injury From Air Bag DeploymentLoads”, published in Accident Analysis & Prevention, Vol 25, No.1, 1993,Pergamon Press, New York, where the authors conclude that “Even aninflator with inadequate gas output to protect a properly seatedoccupant had sufficient energy to induce severe injuries in a surrogatein contact with the inflating module.” These papers highlight theimportance of preventing deployment of an airbag when an occupant is outof position and in close proximity to the airbag module.

The Ball-in-Tube crush zone sensor, such as disclosed in U.S. Pat. Nos.4,974,350; 4,198,864; 4,284,863; 4,329,549; 4,573,706 and 4,900,880 toD. S. Breed, has achieved the widest use while other technologies,including magnetically damped sensors as disclosed in U.S. Pat. No.4,933,515 to Behr et al and crush switch sensors such as disclosed inU.S. Pat. No. 4,995,639 to D. S. Breed, are now becoming available.Other sensors based on spring-mass technologies are also being used inthe crush zone. Crash zone mounted sensors, in order to functionproperly, must be located in the crush zone at the required trigger timeduring a crash or they can trigger late. One example of this wasdisclosed in a Society of Automotive Engineers (SAE) Paper by D. S.Breed and V. Castelli titled “Trends in Sensing Frontal Impacts”, SAE890750, 1989, and further in U.S. Pat. No. 4,900,880. In impacts withsoft objects, the crush of a vehicle can be significantly less than forimpacts with barriers, for example. In such cases, even at moderatevelocity changes where an airbag might be of help in mitigatinginjuries, the crush zone mounted sensor might not actually be in thecrush zone at the time that sensor triggering is required for timelyairbag deployment, and as a result can trigger late when the occupant isalready resting against the airbag module.

There is a trend underway toward the implementation of Single PointSensors (SPS) which are typically located in the passenger compartment.In theory, these sensors use sophisticated computer algorithms todetermine that a particular crash is sufficiently severe as to requirethe deployment of an airbag. In another SAE paper by Breed, Sanders andCastelli titled “A Critique of Single Point Sensing”, SAE 920124, 1992,which is included herein by reference, the authors demonstrate thatthere is insufficient information in the non-crush zone of the vehicleto permit a decision to be made to deploy an airbag in time for manycrashes. Thus, sensors mounted in the passenger compartment or othernon-crush zone locations, will also trigger the deployment of the airbaglate on many crashes.

A crash sensor is necessarily a predictive device. In order to inflatethe airbag in time, the inflation must be started before the fullseverity of the crash has developed. All predictive devices are subjectto error, so that sometimes the airbag will be inflated when it is notneeded and at other times it will not be inflated when it could haveprevented injury. The accuracy of any predictive device can improvesignificantly when a longer time is available to gather and process thedata. One purpose of the occupant position sensor is to make possiblethis additional time in those cases where the occupant is farther fromthe steering wheel when the crash begins and/or where, due to seat beltuse or otherwise, the occupant is moving toward the steering wheel moreslowly. In these cases the decision on whether to deploy the airbag canbe deferred and a more precise determination made of whether the airbagis needed.

The discussions of timely airbag deployment above are all based on theseating position of the average male (the so called 50% male) relativeto the airbag or steering wheel. For the 50% male, the sensor triggeringrequirement is typically calculated based on an allowable motion of theoccupant of 5 inches before the airbag is fully inflated. Airbagstypically require about 30 milliseconds of time to achieve fullinflation and, therefore, the sensor must trigger inflation of theairbag 30 milliseconds before the occupant has moved forward 5 inches.The 50% male, however, is actually the 70% person and therefore about70% of the population sit on average closer to the airbag than the 50%male and thus are exposed to a greater risk of interacting with thedeploying airbag. A recent informal survey, for example, found thatalthough the average male driver sits about 12 inches from the steeringwheel, about 2% of the population of drivers sit closer than 6 inchesfrom the steering wheel and 10% sit closer than 9 inches. Also, about 1%of drivers sit at about 24 inches and about 16% at least 18 inches fromthe steering wheel. None of the sensor systems now on the market takeaccount of this variation in occupant seating position and yet this canhave a critical effect on the sensor required maximum triggering time.

For example, if a fully inflated airbag is about 7 inches thick,measured from front to back, then any driver who is seated closer than 7inches will necessarily interact with the deploying airbag and theairbag probably should not be deployed at all. For a recently analyzed30 mph barrier crash of a mid-sized car, the sensor required triggeringtime, in order to allow the airbag to inflate fully before the driverbecomes closer than 7 inches from the steering wheel, results in amaximum sensing time of 8 milliseconds for an occupant initiallypositioned 9 inches from the airbag, 25 milliseconds at 12 inches, 45milliseconds at 18 inches and 57 milliseconds for the occupant who isinitially positioned at 24 inches from the airbag. Thus for the samecrash, the sensor required triggering time varies from a no trigger to57 milliseconds, depending on the initial position of the occupant. Asingle sensor triggering time criterion that fails to take this intoaccount, therefore, will cause injuries to small people or deny theprotection of the airbag to larger people. A very significantimprovement to the performance of an airbag system will necessarilyresult from taking the occupant position into account as describedherein.

A further complication results from the fact that a greater number ofoccupants are now wearing seatbelts which tends to prevent many of theseoccupants from getting too close to the airbag. Thus, just knowing theinitial position of the occupant is insufficient and either the positionmust be continuously monitored or the seatbelt use must be known. Also,the occupant may have fallen asleep or be unconscious prior to the crashand be resting against the steering wheel. Some sensor systems have beenproposed that double integrate the acceleration pulse in the passengercompartment and determine the displacement of the occupant based on thecalculated displacement of an unrestrained occupant seated at the midseating position. This sensor system then prevents the deployment of theairbag if, by this calculation, the occupant is too close to the airbag.This calculation can be greatly in error for the different seatingpositions discussed above and also for the seatbelted occupant, and thusan occupant who wears a seatbelt could be denied the added protection ofthe airbag in a severe crash.

As the number of vehicles which are equipped with airbags is now rapidlyincreasing, the incidence of late deployments is also increasing. It hasbeen estimated that out of approximately 400 airbag related complaintsto the National Highway Traffic Safety Administration (NHTSA) through1991, for example, about 5% to 10% involved burns and injuries whichwere due to late airbag deployments. There is also at least three knownfatalities where a late airbag deployment is suspected as the cause.

The need for an occupant position sensor has been observed by others andseveral methods have been disclosed in US Patents for determining theposition and velocity of an occupant of a motor vehicle. Each of thesesystems, however, have significant limitations. In White et al., U.S.Pat. No. 5,071,160, for example, a single acoustic sensor and detectoris disclosed and illustrated mounted lower than the steering wheel.White et al correctly perceive that such a sensor could be defeated, andthe airbag falsely deployed, by an occupant adjusting the control knobson the radio and thus they suggest the use of a plurality of suchtransmitter/receivers. If a driver of a vehicle is seated one foot fromthe transmitter/receiver, and using 1128 feet per second as the velocityof sound, it would require approximately 2 milliseconds for the sound totravel to the occupant and return The use of the same device to bothtransmit and detect the sound waves requires that the device cannot sendand receive simultaneously and therefore it requires at least 2milliseconds to obtain a single observation of the occupant's position.Naturally as the distance from the occupant to the sensor increases, theobservation rate further decreases. For a passenger sitting two feetfrom the sensor, the delay is approximately 4 milliseconds. Sensors ofthis type can be used to accurately obtain the initial position of theoccupant but the determination of the occupant's velocity, and thus theprediction of when he/she is likely to be too close to the deployingairbag, will necessarily be inaccurate due to the long delay betweenposition points and thus the small number of such points available forthe prediction and the inherent noise in the reflected signal.

Mattes et al in U.S. Pat. No. 5,118,134 disclose a single ultrasonictransmitter and a separate receiver, but, no description is provided asto the manner in which this combination is used. In conventionalultrasonic distance measuring systems, the transmitter emits a burst ofultrasonic waves and then measures the time required for the waves tobounce off the object and reach the receptor. The transmitter does nottransmit again until the waves have been received by the receiver. Thissystem again suffers from the time delay of at least 2 to 4 millisecondsdescribed above.

Doppler techniques can be used to determine the velocity of the occupantas disclosed below. Both White et al and Mattes et al, however,specifically state that the occupant's velocity is determined from asuccession of position measurements. The use of the Doppler effect isdisclosed in U.S. Pat. No. 3,275,975 to King, but only to determine thatthe occupant is not moving. No attempt is made by King to measure thevelocity of the occupant toward an airbag using this effect. Also noneof the references above disclose the use of an ultrasonic transmitterand receiver to simultaneously determine the position and velocity ofthe occupant using a combination of the transmission time and theDoppler effect as disclosed below.

The object of an occupant position sensor is to determine the locationof the head and/or chest of the vehicle occupant relative to the airbagsince it is the impact of either the head or chest with the deployingairbag which can result in serious injuries. For the purposes herein,therefore, whenever the position of the occupant is referenced it willmean the position of the head or chest of the occupant and not that ofhis/her arms, hands or legs. The preferred mounting of the ultrasonictransmitters, therefore, are those locations which have the clearestunimpeded view of the occupant's head and chest. These locations aregenerally at the top of the dashboard, the windshield, the headlinerabove the windshield and the rear view mirror. Both White et al andMattes et al disclose only lower mounting locations of the ultrasonictransmitters such as on the dashboard or below the steeling wheel. Bothsuch mounting locations are particularly prone to detection errors dueto positioning of the occupant's hands, arms and legs. This wouldrequire at least three, and preferably more, such sensors and detectorsand an appropriate logic circuitry for the case where the driver's armsare the closest objects to two of the sensors. When an unimpeded view isnot possible, some means of pattern recognition, which is not disclosedin the above references, is required to differentiate between theoccupant and his/her extremities such as his/her hands, arms or legs.

Mattes et al further disclose the placement of the sensor in theheadrest but such an arrangement is insufficient since it measures thedistance from the headrest to the occupant and not from the airbag.

White et al discloses the use of error correction circuitry todifferentiate between the velocity of one of the occupant's hands as inthe case where he/she is adjusting the knob on the radio and theremainder of the occupant. Three ultrasonic sensors of the typedisclosed by White et al would accomplish this differentiation if two ofthem indicated that the occupant was not moving while the third wasindicating that he or she was. Such a combination, however, would notdifferentiate between an occupant with both hands and arms in the pathof the ultrasonic transmitter at such a location that it was blocking asubstantial view of the occupant's head or chest. Since the sizes anddriving positions of occupants are extremely varied, pattern recognitionsystems are required when a clear view of the occupant, unimpeded byhis/her extremities, cannot be guaranteed. Pattern recognition systemsfor the occupant as used here means any system which will differentiatebetween the occupant and his extremities based on relative size,position or shape. Pattern recognition systems can also be used todifferentiate an occupant from a seat or a bag of groceries also basedon relative size, position or shape or even on passive infraredradiation, as described below.

OBJECTS AND SUMMARY OF THE INVENTION

The occupant position sensor of this invention is adapted forinstallation in the passenger compartment of an automotive vehicleequipped with a passenger protective device such as an inflatableairbag. When the vehicle is subjected to a crash of sufficient magnitudeas to require deployment of the passive protective device, and thesensor system has determined that the device is to be deployed, theoccupant position sensor and associated electronic circuitry determinesthe position of the vehicle occupant relative to the airbag and disablesdeployment of the airbag if the occupant is positioned so that he/she islikely to be injured by the deploying airbag. Naturally, as discussedbelow, the addition of an occupant position sensor onto a vehicle leadsto other possibilities such as the monitoring of the driver's behaviorwhich can be used to warn a driver if he or she is falling asleep, or tostop the vehicle if the driver loses the capacity to control thevehicle.

According to a preferred implementation, an ultrasonic generatortransmits a burst of ultrasonic waves which travel to the occupant andare reflected back to a receptor, which may be the same device as thegenerator. The time period required for the waves to travel from thegenerator and return is used to determine the position of the occupantand the frequency shift of the waves is used to determine the velocityof the occupant relative to the airbag.

In another preferred implementation, infrared light is used toilluminate the occupant and lenses are used to focus images of theoccupant onto arrays of charge coupled devices (CCD). Outputs from theCCD arrays, are analyzed by appropriate logic circuitry, to determinethe position and velocity of the occupant's head and chest.

In yet another preferred implementation, a beam of radiation is movedback and forth across the occupant illuminating various portions of theoccupant and with appropriate algorithms the position of the occupant inthe seat is accurately determined.

It is a principal object of this invention to provide an occupantposition sensor which reliably permits, and in a timely manner, adetermination to be made that he/she is out of position, or will becomeout of position, and likely to be injured by a deploying airbag.

It is also a principal object of this invention to provide a systemwhich will accurately discriminate between the occupant's head or chestand other parts of the body in determining the occupant's position andvelocity.

It is another object of this invention to independently prevent thedeployment of the driver or passenger airbags if either occupant is outof position.

It is still another object of this invention to provide for a morecomplete analysis of an occupant through the use of CCD's to capturemore of the occupants image.

Another object of this invention is to provide a warning to a driver ifhe/she is falling asleep.

Still another object of this invention is to sense that a driver isinebriated or otherwise suffering from a reduced capacity to operate amotor vehicle and to take appropriate action.

The motor vehicle air bag system for inflation and deployment of an airbag in front of a passenger in a motor vehicle during a collision inaccordance with the invention comprises an air bag, inflation meansconnected to the airbag for inflating the same with a gas, passengersensor means mounted adjacent to the interior roof of the vehicle forcontinuously sensing the position of a passenger with respect to thepassenger compartment and for generating electrical output indicative ofthe position of the passenger and microprocessor means electricallyconnected to the passenger sensor means and to the inflation means. Themicroprocessor means compare and perform an analysis of the electricaloutput from the passenger sensor means and activate the inflation meansto inflate and deploy the air bag when the analysis indicates that thevehicle is involved in a collision and that deployment of the air bagwould likely reduce a risk of serious injury to the passenger whichwould exist absent deployment of the air bag and likely would notpresent an increased risk of injury to the passenger resulting fromdeployment of the air bag. In certain embodiments, the passenger sensormeans is a means particularly sensitive to the position of the head ofthe passenger. The microprocessor means may include memory means forstoring the positions of the passenger over some interval of time. Thepassenger sensor means may comprise an array of passenger proximitysensor means for sensing distance from a passenger to each of thepassenger proximity sensor means. In this case, the microprocessor meansincludes means for determining passenger position by determining each ofthese distances and means for triangulation analysis of the distancesfrom the passenger to each passenger proximity sensor means to determinethe position of the passenger.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodimentstaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing severalpreferred mounting locations of occupant position sensors for sensingthe position of the vehicle driver.

FIG. 2 is a cross section view of a steering wheel and airbag moduleassembly showing a preferred mounting location of an ultrasonic wavegenerator and receiver.

FIG. 3 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing preferredmounting locations of the occupant position sensor employing multipletransmitters and receivers.

FIG. 4 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing an occupantposition sensor used in combination with a reflective windshield forsensing the position of the vehicle passenger.

FIG. 5 is a partial cutaway view of a seatbelt retractor with a spoolout sensor utilizing a shaft encoder.

FIG. 6 is a side view of a portion of a seat and seat rail showing aseat position sensor utilizing a potentiometer.

FIG. 7 is a circuit schematic illustrating the use of the occupantposition sensor in conjunction with the remainder of the inflatablerestraint system.

FIG. 8 is a schematic illustrating the circuit of an occupant positionsensing device using a modulated infrared signal, beat frequency andphase detector system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a section of the passenger compartment ofan automobile is shown generally as 100 in FIG. 1. A driver of a vehicle101 sits on a seat 102 behind a steering wheel 103 which contains anairbag assembly 104. Five transmitter and/or receiver assemblies 110,111, 112, 113 and 114 are positioned at various places in the passengercompartment to determine the location of the head, chest and torso ofthe driver relative to the airbag. Usually, in any given implementation,only one or two of the transmitters and receivers would be useddepending on their mounting locations as described below.

FIG. 1 illustrates several of the possible locations of such devices.For example, transmitter and receiver 110 emits ultrasonic acousticalwaves which bounce off the chest of the driver and return. Periodicallya burst of ultrasonic waves at about 50 kilohertz is emitted by thetransmitter/receiver and then the echo, or reflected signal, is detectedby the same or different device. An associated electronic circuitmeasures the time between the transmission and the reception of theultrasonic waves and thereby determines the distance from thetransmitter/receiver to the driver based on the velocity of sound. Thisinformation is then sent to the crash sensor and diagnostic circuitrywhich determines if the driver is close enough to the airbag that adeployment might, by itself, cause injury to the driver. In such a casethe circuit disables the airbag system and thereby prevents itsdeployment. In an alternate case, the sensor algorithm assesses theprobability that a crash requiring an airbag is in process and waitsuntil that probability exceeds an amount that is dependent on theposition of the occupant. Thus, for example, the sensor might decide todeploy the airbag based on a need probability assessment of 50%, if thedecision must be made immediately for an occupant approaching theairbag, but might wait until the probability rises to 95% for a moredistant occupant. Although a driver system has been illustrated, thepassenger system would be identical.

In another implementation, the sensor algorithm may determine the ratethat gas is generated to affect the rate that the airbag is inflated. Inall of these cases the position of the occupant is used to affect thedeployment of the airbag either as to whether or not it should bedeployed at all, the time of deployment or as to the rate of inflation.

The ultrasonic transmitter/receiver 110 is similar to that used onmodern auto-focus cameras such as manufactured by the PolaroidCorporation. Other camera auto-focusing systems use differenttechnologies, which are also applicable here, to achieve the samedistance to object determination. One camera system manufactured by Fujiof Japan, for example, uses a stereoscopic system which could also beused to determine the position of a vehicle occupant providing there issufficient light available. In the case of insufficient light, a sourceof infrared light can be added to illuminate the driver. In a relatedimplementation, a source of infrared light is reflected off of thewindshield and illuminates the vehicle occupant. An infrared receiver114 is located attached to the rear view mirror 105, as shown in FIG. 1.Alternately, the infrared could be sent by the device 114 and receivedby a receiver elsewhere. Since any of the devices shown in FIGS. 1 and 3could be either transmitters, receivers or both, for simplicity, onlythe transmitted and not the reflected wave fronts are illustrated.

In the above described system a lens within receptor 114 captures thereflected infrared light from the head or chest of the driver anddisplays it onto a charge coupled device (CCD) array. One type of CCD isthat used in television cameras to convert an image into an electricalsignal. For the purposes herein a CCD will be used to include alldevices which are capable of converting light frequencies, includinginfrared, into electrical signals. The CCD is scanned and the focalpoint of the lens is altered, under control of an appropriate circuit,until the sharpest image of the driver's head or chest results and thedistance is then known from the focusing circuitry. The precision ofthis measurement is enhanced if two receptors are used which can eitherproject images onto a single CCD or on separate CCDs. In the first case,one of the lenses could be moved to bring the two images intocoincidence while in the other case the displacement of the imagesneeded for coincidence would be determined mathematically. Naturally,other systems could be used to keep track of the different images suchas the use of filters creating different infrared frequencies for thedifferent receptors and again using the same CCD array. In addition togreater precision in determining the location of the occupant, theseparation of the two receptors can also be used to minimize the effectsof hands, arms or other extremities which might be very close to theairbag. In this case, where the receptors are mounted high on thedashboard on either side of the steering wheel, an arm, for example,would show up as a thin object but much closer to the airbag than thelarger body parts and, therefore, easily distinguished and eliminated,permitting the sensors to determine the distance to the occupant'schest. This is one example of the use of pattern recognition.

An optical infrared transmitter and receiver assembly is shown generallyat 112 in FIG. 1 and is mounted onto the instrument panel facing thewindshield. Although not shown in this view, reference 112 consists ofthree devices, one transmitter and two receivers, one on each side ofthe transmitter. In this case the windshield is used to reflect theillumination light, and also the light reflected back by the driver, ina manner similar to the “heads-up” display which is now being offered onseveral automobile models. The “heads-up” display, of course, iscurrently used only to display information to the driver and is not usedto reflect light from the driver to a receiver. In this case thedistance to the driver is determined stereoscopically through the use ofthe two receivers. In its most elementary sense, this system can be usedto measure the distance of the driver to the airbag module. In moresophisticated applications, the position of the driver, and particularlyof the drivers head, can be monitored over time and any behavior, suchas a drooping head, indicative of the driver falling asleep or of beingincapacitated by drugs, alcohol or illness can be detected andappropriate action taken. Other forms of radiation including visuallight, radar and microwaves as well as high frequency ultra sound couldalso be used by those skilled in the art.

Particular mention should be made of the use of radar since inexpensivesingle axis antennas are now readily available. A scanning radar beam isused in this implementation and the reflected signal is received by asingle axis phase array antenna to generate an image of the occupant forinput into the appropriate pattern detection circuitry. The wordcircuitry as used herein includes, in addition to normal electroniccircuits, a microprocessor and appropriate software.

Electromagnetic or ultrasonic energy can be transmitted in three modesin determining the position of an occupant. In most of the casesdisclosed above, it is assumed that the energy will be transmitted in abroad diverging beam which interacts with a substantial portion of theoccupant. This method has the disadvantage that it will reflect firstoff the nearest object and, especially if that object is close to thetransmitter, it may mask the true position of the occupant. This can bepartially overcome through the use of the second mode which uses anarrow beam. In this case, several narrow beams are used. These beamsare aimed in different directions toward the occupant from a positionsufficiently away from the occupant that interference is unlikely. Asingle receptor could be used providing the beams are either cycled onat different times or are of different frequencies. Another approach isto use a single beam emanating from a location which has an unimpededview of the occupant such as the windshield header. If two spaced apartCCD array receivers are used, the angle of the reflected beam can bedetermined and the location of the occupant can be calculated. The thirdmode is to use a single beam in a manner so that it scans back and forthor up and down, or in some other pattern, across the occupant. In thismanner, an image of the occupant can be obtained using a single receptorand pattern recognition software can be used to locate the head or chestof the occupant. The beam approach is most applicable to electromagneticenergy but high frequency ultra sound can also be formed into a narrowbeam.

The windshield header as used herein includes the space above the frontwindshield including the first few inches of the roof.

A similar effect to modifying the wave transmission mode can also beobtained by varying the characteristics of the receptors. Throughappropriate lenses or reflectors, receptors can be made to be mostsensitive to radiation emitted from a particular direction. In thismanner a single broad beam transmitter can be used coupled with an arrayof focused receivers to obtain a rough image of the occupant.

Each of these methods of transmission or reception could be used, forexample, at any of the preferred mounting locations shown in FIG. 1.

Another preferred location of a transmitter/receiver for use withairbags is shown at 111 in FIG. 1. In this case the device is attachedto the steering wheel and gives an accurate determination of thedistance of the driver's chest from the airbag module. Thisimplementation would generally be used with another device such as 110at another location.

Alternate mountings for the transmitter/receiver include variouslocations on the instrument panel on either side of the steering columnsuch as 113 in FIG. 1. Also, although some of the devices hereinillustrated assume that for the ultrasonic system the same device wouldbe used for both transmitting and receiving waves, there are advantagesin separating these functions. Since there is a time lag required forthe system to stabilize after transmitting a pulse before it can receivea pulse, close measurements are enhanced, for example, by using separatetransmitters and receivers. In addition, if the ultrasonic transmitterand receiver are separated, the transmitter can transmit continuouslyproviding the transmitted signal is modulated in such a manner that thereceived signal can be compared with the transmitted signal to determinethe time it took for the waves to reach and reflect off of the occupant.Many methods exist for this modulation including varying the frequencyor amplitude of the waves or by pulse modulation or coding. In allcases, the logic circuit which controls the sensor and receiver must beable to determine when the signal which was most recently received wastransmitted. In this manner, even though the time that it takes for thesignal to travel from the transmitter to the receiver, via reflectionoff of the occupant, may be several milliseconds, information as to theposition of the occupant is received continuously which permits anaccurate, although delayed, determination of the occupant's velocityfrom successive position measurements. Conventional ultrasonic distancemeasuring devices must wait for the signal to travel to the occupant andreturn before a new signal is sent. This greatly limits the frequency atwhich position data can be obtained to the formula where the frequencyis equal two times the distance to the occupant divided by the velocityof sound. For example, if the velocity of sound is taken at about 1000feet per second, occupant position data for an occupant located one footfrom the transmitter can only be obtained every 2 milliseconds.

This slow frequency that data can be collected seriously degrades theaccuracy of the velocity calculation. The reflection of ultrasonic wavesfrom the clothes of an occupant, for example, can cause noise or scatterin the position measurement and lead to significant inaccuracies in agiven measurement. When many measurements are taken more rapidly, as inthe technique described here, these inaccuracies can be averaged and asignificant improvement in the accuracy of the velocity calculationresults.

The determination of the velocity of the occupant need not be derivedfrom successive distance measurements. A potentially more accuratemethod is to make use of the Doppler effect where the frequency of thereflected waves differs from the transmitted waves by an amount which isproportional to the occupant's velocity. In a preferred embodiment ofthe present invention, a single ultrasonic transmitter and a separatereceiver are used to measure the position of the occupant, by the traveltime of a known signal, and the velocity, by the frequency shift of thatsignal. Although the Doppler effect has been used to determine whetheran occupant has fallen asleep as disclosed in the U.S. Patent to Kingreferenced above, it has not heretofore been used in conjunction with aposition measuring device to determine whether an occupant is likely tobecome out of position and thus in danger of being injured by adeploying airbag. This combination is particularly advantageous sinceboth measurements can be accurately and efficiently determined using asingle transmitter and receiver pair resulting in a low cost system.

Another preferred embodiment of this invention makes use of radio wavesand a voltage controlled oscillator (VCO). In this implementation, thefrequency of the oscillator is controlled through the use of a phasedetector which adjusts the oscillator frequency so that exactly one halfwave occupies the distance from the transmitter to the receiver viareflection off of the occupant. The adjusted frequency is thus inverselyproportional to the distance from the transmitter to the occupant.Alternately, an FM phase discriminator can be used as known to thoseskilled in the art. These systems could be used in any of the locationsillustrated in FIG. 1.

It was suggested in the U.S. patent to Mattes et al. discussed above,that a passive infrared system could be used to determine the positionof an occupant relative to an airbag. Passive infrared measures theinfrared radiation emitted by the occupant and compares it to thebackground. As such, unless it is coupled with a pattern recognitionsystem, it can best be used to determine that an occupant is movingtoward the airbag since the amount of infrared radiation would then beincreasing. Therefore, it could be used to estimate the velocity of theoccupant but not his/her position relative to the airbag, since theabsolute amount of such radiation will depend on the occupant's size,temperature and clothes as well as on his position. When passiveinfrared is used in conjunction with another distance measuring system,such as the ultrasonic system described above, the combination would becapable of determining both the position and velocity of the occupantrelative to the airbag. Such a combination would be economical sinceonly the simplest circuits would be required. In one implementation, forexample, a group of waves from an ultrasonic transmitter could be sentto an occupant and the reflected group received by a receiver. Thedistance to the occupant would be proportional to the time between thetransmitted and received groups of waves and the velocity determinedfrom the passive infrared system. This system could be used in any ofthe locations illustrated in FIG. 1 as well as others not illustrated.

Passive infrared could also be used effectively in conjunction with apattern recognition system. In this case, the passive infrared radiationemitted from an occupant can be focused onto a CCD array and analyzedwith appropriate pattern recognition circuitry, or software, todetermine the position of the occupant. Such a system could be mountedat any of the preferred mounting locations shown in FIG. 1 as well asothers not illustrated.

A transmitter/receiver 215 shown mounted on the cover of the airbagmodule is shown in FIG. 2. The transmitter/receiver 215 is attached tovarious electronic circuitry, not shown, by means of wire cable 212.When an airbag deploys, the cover 220 begins moving toward the driver.If the driver is in close proximity to this cover during the earlystages of deployment, the driver can be seriously injured or evenkilled. It is important, therefore, to sense the proximity of the driverto the cover and if he or she gets too close, to disable deployment ofthe airbag. An accurate method of obtaining this information would be toplace the distance measuring device onto the airbag cover as is shown inFIG. 2. Appropriate electronic circuitry can be used to not onlydetermine the actual distance of the driver from the cover but also hisvelocity as discussed above. In this manner, a determination can be madeas to where the driver is likely to be at the time of deployment of theairbag. This information can be used most importantly to preventdeployment but also to modify the rate of airbag deployment. In FIG. 2,for one implementation, ultrasonic waves are transmitted by atransmitter/receiver 215 toward the chest 222 of the driver. Thereflected waves are then received by the same transmitter/receiver 215.

One problem of the system using a sensor 111 in FIG. 1 or sensor 215 asshown in FIG. 2 is that a driver may have inadvertently placed his handover the transmitter/receiver 111 or 215, thus defeating the operationof the device. A second confirming transmitter/receiver 110 is thereforeplaced at some other convenient position such as on the roof orheadliner of the passenger compartment as shown in FIG. 3. Thistransmitter/receiver operates in a manner similar to 111 and 215.

A more complicated and sophisticated system is shown conceptually inFIG. 4 where transmitter/receiver assembly 112 is illustrated. In thiscase, as described briefly above, an infrared transmitter and a pair ofoptical receivers are used to capture the reflection of the passenger.When this system is used to monitor the driver as shown in FIG. 4, withappropriate circuitry and a microprocessor, the behavior of the drivercan be monitored. Using this system, not only can the position andvelocity of the driver be determined and used in conjunction with anairbag system, but it is also possible to determine whether the driveris falling asleep or exhibiting other potentially dangerous behavior bycomparing portions of his/her image over time. In this case the speed ofthe vehicle can be reduced or the vehicle even stopped if this action isconsidered appropriate. This implementation has the highest probabilityof an unimpeded view of the driver since he/she must have a clear viewthrough the windshield in order to operate the motor vehicle.

As discussed above, a primary object of this invention is to provideinformation as to the location of the driver, or other vehicle occupant,relative to the airbag, to appropriate circuitry which will process thisinformation and make a decision as to whether to prevent deployment ofthe airbag in a situation where it would otherwise be deployed, orotherwise affect the time of deployment. One method of determining theposition of the driver as discussed above is to actually measure his orher position either using microwaves, optics or acoustics. An alternateapproach, which is preferably used to confirm the measurements made bythe systems described above, is to use information about the position ofthe seat and the seatbelt spool out to determine the likely location ofthe driver relative to the airbag. To accomplish this the length of beltmaterial which has been pulled out of the seatbelt retractor can bemeasured using conventional shaft encoder technology using eithermagnetic or optical systems. An example of an optical encoder isillustrated generally as 501 in FIG. 5. It consists of an encoder disk502 and a receptor 503 which sends a signal to appropriate circuitryevery time a line on the encoder disk passes by the receptor.

In a similar manner, the position of the seat can be determined througheither a linear encoder or a potentiometer as illustrated in FIG. 6. Inthis case, a potentiometer 601 is positioned along the seat track 602and a sliding brush assembly 603 is used with appropriate circuitry todetermine the fore and aft location of the seat 610. Naturally, forthose seats which permit the seat back angle to be adjusted, a similarmeasuring system would be used to determine the angle of the seat back.In this manner the position of the seat relative to the airbag modulecan be determined. This information can be used in conjunction with theseatbelt spool out sensor to confirm the approximate position of thechest of the driver relative to the airbag.

For most cases the seatbelt spool out sensor would be sufficient to givea good confirming indication of the position of the occupant's chestregardless of the position of the seat and seat back. This is becausethe seatbelt is usually attached to the vehicle at least at one end. Insome cases, especially where the seat back angle can be adjusted,separate retractors would be used for the lap and shoulder portions ofthe seatbelt and the belt would not be permitted to slip through the“D-ring”. The length of belt spooled out from the shoulder beltretractor then becomes a very good confirming measure of the position ofthe occupant's chest.

The occupant position sensor in any of its various forms can beintegrated into the airbag system circuitry as shown schematically inFIG. 7. In this example, the occupant position sensors are used as aninput to a smart electronic sensor and diagnostic system. The electronicsensor determines whether the airbag should be deployed based on thevehicle acceleration crash pulse, or crush zone mounted crash sensors,and the occupant position sensor determines whether the occupant is tooclose to the airbag and therefore that the deployment should not takeplace.

A particular implementation of an occupant position sensor having arange of from 0 to 2 meters (corresponding to an occupant position offrom 0 to 1 meter since the signal must travel both to and from theoccupant) using infrared is illustrated in the block diagram schematicof FIG. 8. The operation is as follows. A 48 MHz signal, f1, isgenerated by a crystal oscillator 801 and fed into a frequency tripler802 which produces an output signal at 1.44 MHz. The 1.44 MHz signal isthen fed into an infrared diode driver 803 which drives the infrareddiode 804 causing it to emit infrared light modulated at 144 MHz and areference phase angle of zero degrees. The infrared diode 804 isdirected at the vehicle occupant. A second signal f2 having a frequencyof 48.05 Mhz, which is slightly greater than f1, is also fed into afrequency tripler 806 to create a frequency of 144.15 Mhz. This signalis then fed into a mixer 807 which combines it with the 144 MHz signalfrom frequency tripler 802. The combined signal from the mixer 807 isthen fed to filter 808 which removes all signals except for thedifference, or beat frequency, between 3 times f1 and 3 times f2, of 150KHz. The infrared signal which is reflected from the occupant isreceived by receiver 809 and fed into pre-amplifier 811. This signal hasthe same modulation frequency, 144 MHz, as the transmitted signal butnow is out of phase with the transmitted signal by an angle x due to thepath that the signal took from the transmitter to the occupant and backto the receiver. The output from pre-amplifier 811 is fed to a secondmixer 812 along with the 144.15 MHz signal from the frequency tripler806. The output from mixer 812 is then amplified by the automatic gainamplifier 813 and fed into filter 814. The filter 814 eliminates allfrequencies except for the 150 KHz difference, or beat, frequency in asimilar manner as was done by filter 808. The resulting 150 KHzfrequency, however, now has a phase angle x relative to the signal fromfilter 808. Both 150 KHz signals are now fed into a phase detector 815which determines the magnitude of the phase angle x. It can be shownmathematically that, with the above values, the distance from thetransmitting diode to the occupant is x/345.6 where x is measured indegrees and the distance in meters.

The applications described herein have been illustrated using the driverof the vehicle. Naturally the same systems of determining the positionof the occupant relative to the airbag apply to the passenger, sometimesrequiring minor modifications. It is likely that the sensor requiredtriggering time based on the position of the occupant will be differentfor the driver than for the passenger. Current systems are basedprimarily on the driver with the result that the probability of injuryto the passenger is necessarily increased either by deploying the airbagtoo late or by failing to deploy the airbag when the position of thedriver would not warrant it but the passenger's position would. With theuse of occupant position sensors for both the passenger and driver, theairbag system can be individually optimized for each occupant and resultin further significant injury reduction. In particular, either thedriver or passenger system can be disabled if either the driver orpassenger is out of position.

There is almost always a driver present in vehicles that are involved inaccidents where an airbag is needed. Only about 30% of these vehicles,however, have a passenger. if the passenger is not present, there isusually no need to deploy the passenger side airbag. The occupantposition sensor, when used for the passenger side with proper patternrecognition circuitry, can also ascertain whether or not the seat isoccupied, and if not can disable the deployment of the passenger sideairbag and thereby save the cost of its replacement. A sophisticatedpattern recognition system could even distinguish between an occupantand a bag of groceries, for example. Finally, there has been muchwritten about the out of position child who is standing or otherwisepositioned adjacent to the airbag, perhaps due to pre-crash braking.Naturally, the occupant position sensor described herein can prevent thedeployment of the airbag in this situation.

There has thus been shown and described an occupant position sensorwhich fulfills all the objects and advantages sought after. Manychanges, modifications, variations and other uses and applications ofthe subject invention will, however, become apparent to those skilled inthe art after considering this specification and the accompanyingdrawings which disclose the preferred embodiments thereof. All suchchanges, modifications, variations and other uses and applications whichdo not depart from the spirit and scope of the invention are deemed tobe covered by the invention which is limited only by the followingclaims.

What is claimed is:
 1. Motor vehicle air bag system, for inflation anddeployment of an air bag in front of a passenger in a motor vehicleduring a collision, said motor vehicle having a passenger compartmentfor at least one passenger in said motor vehicle, said passengercompartment also having an interior roof, and having a windshield at theforward end of said passenger compartment, and having a passenger seatfor said passenger, said airbag system comprising: (a) an air bag; (b)inflation means, connected to said airbag, for inflating said air bagwith a gas; (c) passenger sensor means, mounted adjacent to saidinterior roof of said vehicle, for continuously sensing position of saidpassenger, with respect to said passenger compartment, and forgenerating electrical output indicative of said position of saidpassenger; (d) microprocessor means, electrically connected to saidpassenger sensor means and to said inflation means, for comparing andperforming an analysis of said electrical output from said passengersensor means, and for activating said inflation means to inflate anddeploy said air bag, when said analysis indicates that said vehicle isinvolved in a collision and that deployment of said air bag would likelyreduce a risk of serious injury to said passenger which would existabsent deployment of said air bag and likely would not present anincreased risk of injury to said passenger resulting from deployment ofsaid air bag.
 2. The motor vehicle air bag system of claim 1, whereinsaid passenger sensor means comprises an array of passenger proximitysensor means, for sensing distance from a passenger to each of saidpassenger proximity sensor means, and wherein said microprocessor meansincludes means for determining passenger position by determining each ofsaid distances, and further includes means for triangulation analysis ofthe distances from said passenger to each of said passenger proximitysensor means, to determine the position of said passenger.
 3. The motorvehicle air bag system of claim 1, wherein said microprocessor meansincludes memory means for storing said positions of said passenger oversome interval of time.
 4. The motor vehicle air bag system of claim 1,wherein said passenger sensor means is a means particularly sensitive tothe position of the head of said passenger.
 5. In a motor vehicle havingan air bag module including an inflatable airbag and inflation means forinflating the air bag in front of an occupant of the motor vehicleduring a collision, an airbag control system comprising: sensor meansmounted adjacent to an interior roof of the vehicle for sensing theposition of the occupant with respect to the passenger compartment ofthe vehicle and for generating output indicative of the position of theoccupant; and microprocessor means connected to said sensor means and tothe inflation means for comparing and performing an analysis of saidoutput from said sensor means and activating the inflation means toinflate the air bag, when said analysis indicates that the vehicle isinvolved in a collision and deployment of the air bag is desired.
 6. Theairbag control system of claim 5, wherein said sensor means comprises anarray of occupant proximity sensor means for sensing distance from theoccupant to each of said proximity sensor means, and wherein saidmicroprocessor means includes means for determining the occupant'sposition by determining each of said distances, and further includesmeans for triangulation analysis of the distances from the occupant toeach of said proximity sensor means, to determine the position of theoccupant.
 7. The airbag control system of claim 5, wherein saidmicroprocessor means includes memory means for storing said positions ofthe occupant over some interval of time.
 8. The airbag control system ofclaim 5, wherein said sensor means is a means particularly sensitive tothe position of the head of the occupant.
 9. The airbag control systemof claim 5, wherein the occupant is seated on a passenger seat of thevehicle and said sensor means are structured and arranged to sense theposition of the occupant on the passenger seat.